August 22, 2012

Are Canada's stick builders ready for CLT?

Construction Corner | Korky Koroluk

Canada is sometimes said to have the best housing stock in the world. We build good houses and the reason they're so good is that we've had stringent building codes for a long time.

The result, boosters say, is that Canadians have become “the best stick builders in the world.”

Most of our houses, of course, are built of sticks — 2x4s, chipboard, trim, even cedar shingles on the roof at times.

Having been at it for generations, we’ve become very good at it.

Which makes me wonder why we are slow in adopting the concept of building with bigger structural members made of wood — members that would allow us to produce tall wooden buildings.

The technology is out there in the form of cross-laminated timber (CLT) beams and panels, and their use is growing in some parts of the world.

In North America, we have one low CLT building nearing completion on the campus of the University of British Columbia, and another low building (for a martial arts studio) in Whitefish, Mont. And that’s about it.

In the meantime, an eight-storey CLT office building is almost completed in Austria, and a 10-storey CLT apartment building is under way in Australia.

In England there is the three-year-old Graphite Apartments building (originally called Stadthaus), a nine-storey structure made of prefabricated CLT members bolted together on site.

And Waugh Thistleton, the architectural firm that designed the Graphite, has a four-storey mixed-use building under construction nearby, and an eight-storey apartment building underway within walking distance of the first two.

They, and other architects, are talking about CLT buildings of 10, 15, even 30 storeys — although those very tall buildings would likely be hybrids, with a concrete core.

The spruce timber panels — many of them 15 or more centimetres thick — used in Waugh Thistleton’s buildings were prefabricated in Austria, and form the exterior and interior walls, floors and roof.

Even the stairwells and elevator shafts are made from the panels.

CLT beams and panels were developed in Europe about 20 years ago, so it’s no surprise that they have been used in many — mostly low — structures.

Building codes in some European nations restrict wooden buildings to four storeys, although that is changing.

“Codes” is the key word. Where codes permit, CLT is becoming popular. And until code-writing organizations fully understand the properties of CLT, they’re reluctant to admit it into the codes.

The knock against wood construction is the fear of fire. But, laminated members are, because of their dimensions, difficult to ignite.

A lot of fire testing has been done and that’s why European authorities are now comfortable writing CLT into their codes. Many structural engineers are not familiar with CLT, so there is a learning curve for them.

It’s not the same building with CLT as it is with timber frame, and loads are distributed differently.

Anthony Thistleton, a partner in Waugh Thistleton, has been quoted as saying that “one of the things we found difficult to get across (is) that timber panel construction is completely different from timber frame.”

“It’s got more in common with precast concrete construction,” he said.

The building on the UBC campus is for the university’s bioresearch and demonstration project.

It’s a four-storey structure of 1,886 square metres, and is the first North American commercial application of CLT.

As a first CLT building, it will be watched by architects, structural engineers, fire engineers and developers.

Environmental scientists will be watching, too, because building with wood is more friendly to the world around us than building with concrete or steel. Should it gain acceptance and should building codes make it easier to use, building with cross-laminated timber could become another form of “stick building” for Canadians to use.

Korky Koroluk is a regular freelance contributor to the Journal of Commerce. Send comments or questions to editor@journalofcommerce.com.

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